As the image fluctuation correction device for correcting fluctuation of taken image, there has been conventionally known a camera whose main body has a built-in function of correcting fluctuation of images at filming. Patent Document No. 1 (Japanese Patent Publication Laid-open No. 9-51469) proposes a technique of utilizing a prism as one method of correcting this image fluctuation.
An active prism used in this technique has a structure where two sheets of glass plates are connected to each other through an expandable bellows of special film, and liquid having a refraction index generally equal to that of the glasses is charged between the glass plates. This active prism is arranged between a CCD image sensor and an objective lens of a lens unit which leads a subject image from the objective lens on the front side of a video camera body to the CCD image sensor. By changing respective tilting angles of respective glass plates to the video camera body in a vertical or a horizontal direction, the active prism is adapted so as to correct the image fluctuation.
However, in a device for correcting image fluctuation with the use of a refractive element, such as the image fluctuation correction device described in Patent Document No. 1, as the correction of image fluctuation is carried out through the use of refraction index, chromatic aberration is produced in an optical image due to different refraction indexes every wavelengths. Consequently, as the so-taken image is apt to be shifted with respect to each color thereby to cause its deterioration (referred to as “image shift” hereinafter), it has been impossible to provide an image taken for a user in the form of a vivid image.
It is therefore considered to correct this chromatic aberration optically. However, while the use of a normal lens causes chromatic aberration to be radially produced about its optical axis as a center, the use of a device for correcting image fluctuation by a prism would produce chromatic aberration in one direction irrespective of the optical axis and furthermore, the direction of chromatic aberration varies to an opposite direction temporally. Thus, it has been difficult to optically correct the chromatic aberration like a normal lens.
As the still image acquisition device for acquiring a still image from taken images, in addition, there is generally known a device that acquires a still image from taken images immediately after receiving a still image acquisition signal inputted by a user.
However, when using a general still image acquisition device to acquire a general still image from images corrected by the image fluctuation correction device described in Patent Document No. 1, the refraction angle of incident light gets larger as the correction amount against the fluctuation of an image is increased. As a result, the still image acquired with such an increased refraction angle has an increased image shift due to chromatic aberration.
Therefore, in the general still image acquisition device mentioned above, if receiving the still image acquisition signal under condition that the correction amount of the image fluctuation is maximum, then the image shift due to chromatic aberration in the acquisition image is maximized to preclude an acquisition of a clear still image.
On the assumption of providing a threshold value in terms of the angle change in taking moving images, therefore, Patent Document No. 2 (Japanese Patent Publication No. 3548308) proposes an imaging device that is constructed so as to allow an acquisition of a still image when the actual angle change is less than the threshold value.